The present invention relates to a video display apparatus composed of light-emitting elements such as light-emitting diodes or the like.
There have been developed video display apparatus composed of light-emitting elements such as light-emitting diodes (LED) or the like for displaying images.
FIG. 1 of the accompanying drawings shows a display panel of an LED video display apparatus. As shown in FIG. 1, the display panel of the LED video display apparatus, generally designated by the reference numeral 1, has a dot matrix of LEDs 2 disposed respectively at positions each indicated by a circle and mounted on an LED matrix board 3.
In the illustrated LED video display apparatus 1, the display panel is composed of 16 vertical arrays.times.16 horizontal arrays=256 LEDs. Actually, however, a number of such display panels are combined into a large-size display panel for displaying large images. For full-color image display, pixels each composed of blue, red, and green LEDs are arranged in a matrix on X- and Y-axes.
FIG. 2 of the accompanying drawings illustrates a known structure for each of the LEDs 2 in the LED video display apparatus 1. As shown in FIG. 2, the LED 2 comprises a pellet 2b encased in a molded resin cover 2a in the shape of a lens which is symmetric with respect to an optical axis thereof. The resin cover 2a may be molded of an epoxy resin, for example.
The pellet 2b, which is a light-emitting body, comprises a semiconductor PN junction, and emits light in a color determined by the material and shape of the semiconductor of the PN junction. The pellet 2b is disposed in a reflector R formed on an electrode lead 2d, and connected to another electrode lead 2d by a bonding wire 2c.
Light emitted substantially horizontally from the pellet 2b is reflected forwardly by the reflector R disposed around the pellet 2b, and is discharged from the LED 2 with relatively narrow directivity by the action of the axis-symmetric lens of the resin cover 2a.
Since the light discharged from each of the LEDs 2 is refracted by the lens so as to converge substantially along the optical axis thereof, the LED video display apparatus 1 is highly luminous when it is viewed from its front side.
LED video display apparatus with large-size display panels are usually used in such conditions that their vertical angle of view is not required to be large, but at least the horizontal angle of view should preferably be as large as possible.
The LED video display apparatus 1 which is composed of the LEDs 2 shown in FIG. 2 can produce a high level of luminosity because the directivity of LEDs 2 is relatively narrow. However, the luminosity of the LED video display apparatus is lower, i.e., the angle of view thereof is smaller, when it is viewed from directions other than the front side thereof.
The process of manufacturing the LED video display apparatus 1 is complex because the LEDs 2 are attached to the LED matrix board 3 by inserting and soldering the electrode leads 2d of the LEDs 2 in lead holes which are defined in the LED matrix board 3.
FIG. 3 of the accompanying drawings shows a surface-mounted LED 2 different from the LED 2 shown in FIG. 2. Those parts of the surface-mounted LED 2 shown in FIG. 3 which are identical to those of the LED 2 shown in FIG. 2 are denoted by identical reference characters.
As shown in FIG. 3, the surface-mounted LED 2 comprises a pellet 2b mounted on an electrode 2d disposed on a base 2e and a block-shaped resin cover 2a molded around the pellet 2b, the pellet 2b being connected to another electrode 2d by a bonding wire 2c. The surface-mounted LED 2 has no reflector for reflecting light emitted from the pellet 2b in a forward direction, and the resin cover 2a is not in the shape of a lens for converging the emitted light. Therefore, the surface-mounted LED 2 emits in a diffused pattern, i.e., has relatively wide directivity. The base 2e carries a cathode mark KM on one end thereof, indicating that the electrode 2d near the cathode mark KM is a cathode electrode.
The surface-mounted LED 2 can be manufactured more easily than the LED 2 shown in FIG. 2 because the LED 2 may be placed in position on an LED matrix board and soldered thereby by reflow soldering. The relatively wide directivity of the surface-mounted LED 2 allows the video display apparatus incorporating the same to have wide angles of view in both vertical and horizontal directions. However, the relatively wide directivity of the surface-mounted LED 2 also poses a problem because the emitted light is diffused and the video display apparatus cannot produce a high level of luminosity.